Jacksonville Jaguars quarterback Blake Bortles (5) drops back to pass against the Chicago Bears during the third quarter of the preseason game at Soldier Field. / Mike Dinovo, USA TODAY Sports

by Erik Brady and Jim Corbett, USA TODAY Sports

by Erik Brady and Jim Corbett, USA TODAY Sports

Once upon a time, children were admonished to be seen, not heard. Likewise, rookie quarterbacks were to be seen carrying a clipboard, not heard barking out signals. The idea was tender young QBs should sit behind their elders and take time to learn the faster, more cerebral pro game.

Such thinking is so last millennium. When the NFL season begins in a few weeks, roughly one-quarter of the league's 32 teams, give or take, figure to be led by quarterbacks in their first, second or third years.

In the past few days, Blake Bortles in Jacksonville and Teddy Bridgewater in Minnesota, rookies both seemingly destined to open the season on the bench, have played well enough in the preseason to potentially change plans in both cities. Meanwhile in Cleveland the quarterback competition of the summer continues to rage between rookie Johnny Manziel and veteran Brian Hoyer.

The Browns have been telling the world since drafting Manziel in May that he's their backup, and indeed he will follow Hoyer on Monday when the team plays the Washington Redskins (8 p.m. ET, ESPN). But the world does not want to hear this. TV ratings show the world wants to watch Johnny Football.

McCown, 35, is a journeyman playing for his eighth NFL team. "Back in 2004, I had an old-school scout tell me it takes five years to develop a quarterback," he says. "But now you have Matt Ryan, Joe Flacco, Russell Wilson and Andrew Luck and Robert Griffin III do what they did and everybody goes, 'Whoa.'"

Second-year Philadelphia Eagles quarterback Nick Foles threw 27 TD passes and two interceptions last season, best ratio in NFL history, and he had a perfect passer rating with seven TDs in his third start. Double whoa.

"It has just all been a progression, so it's not like a big shock," Foles says of his growth. "It's not like one day I was just a rookie sitting on the sidelines and the next day I'm just thrown in as a starter; that's a shock. It has progressed to where it just feels natural."

In the old days, quarterbacks might not be seasoned enough to be full-time starters by their third seasons. Now if QBs haven't blossomed by then, teams often give up on them.

"Yeah, three seasons, same staff, same playbook, same everything, you know" if they're going to make it, Jacksonville Jaguars offensive coordinator Jedd Fisch says.

Miami Dolphins coach Joe Philbin thinks that's enough time. He figures starting quarterbacks get about 1,000 reps a season and "if you have 3,000 snaps under your belt, you should have a pretty good idea. â?¦ Especially the way the CBA is, you'd definitely like to know what you have after three years," a reference to the collective bargaining agreement that allows a rookie wage scale and four-year deals for first-round draft choices.

All of which makes this potentially a make-or-break season for Dolphins quarterback Ryan Tannehill, entering his third season. The Dolphins drafted him eighth overall in 2012, the first time they'd taken a quarterback in the first round since Dan Marino in 1983.

"Your first year, you're just trying to do the best you can," Tannehill says. "You're learning how the NFL works, how the season works, new offense, new team. And going into your second year, you're building on that. Now you have an idea how things go. Now you're working all offseason on your game, connecting with guys, bringing the team together.

"Now going into your third year, new offense, it's really about stepping forward as a leader - being the guy that everyone looks to on the team to win games. I want that pressure on my shoulders to go win games. Now it's a matter of doing it."

GETTING UP TO SPEED

The hardest part for young quarterbacks entering the NFL is the speed of the pro game.

"It's so much faster than college and high school," Jaguars quarterback Chad Henne says. "When you see a window that looks open, it's very, very tight."

Fisch points to the "catch-up speed" of NFL cornerbacks: "Guys are never really open. You have to throw them open and you have to trust that your receiver will catch the ball if it's one on one. We tell our guys, 'Hey, if one guy is covering him, he's open. If two guys are covering him, you have to move on.'"

Caldwell draws a distinction between the speed young QBs are seeing during preseason games and what they'll face in a few weeks: "There's a different speed for a rookie in the regular season, when you have to make decisions that much faster. And then, (with experience) the game finally slows down."

Henne, entering his seventh season, is the Jaguars' starter, for now. As in Cleveland, Jacksonville fans are anxious for the mantle to be passed. Bortles, third overall pick and first QB taken in the 2014 draft, got a standing ovation in his first preseason game and followed that by completing 11-for-17 passes for 160 yards against Chicago on Thursday. Coach Gus Bradley said Sunday Bortles will get some first-team practice time today.

"If they don't understand protections and they're not sure who might be a free hitter coming at me, it's real easy to lose their confidence because they're getting hit all the time," Olson says. "Anytime you're getting hit, now your feet are out of place, you're playing skittish with your feet."

"Everything that we do in practice, it's hands-off on the quarterback," Olson says. "So, you're never exactly sure how a guy's going to react once the live bullets start coming."

YEAR ONE TO YEAR TWO

There is no set way to develop a quarterback. Peyton Manning started as a rookie in Indianapolis in 1998 and threw 26 TD passes, most for a rookie in NFL history. Aaron Rodgers sat behind Brett Favre in Green Bay for three seasons before emerging as a starter and one of the league's biggest stars.

"I don't believe in one way or the other," Caldwell says. "I just believe it depends on the person and the situation. â?¦ Whereas some quarterbacks will come in ready to play right away where some guys need time to develop and mature. "

Caldwell witnessed Manning's rookie season in Indy and Matt Ryan's in Atlanta. He points out "both those guys spent five years in college. And they played in pro-style offenses. There's a lot of (other) guys who struggled" playing early.

Blaine Gabbert, for instance, 10th overall pick in the 2011 draft by the Jaguars, is seen as a bust. Fisch blames a lack of continuity.

"Blaine Gabbert, three years, three offensive coordinators, three head coaches, three quarterback coaches," Fisch says of the 10th overall pick in the 2011 draft. "If you look at the quarterbacks who have had the biggest success, they've been in a consistent system. One of the things that has happened to these young quarterbacks that might not have made it, there's been a ton of turnover."

How much does a young quarterback learn from year to year? "It's hard to quantify that one," McCown says. "Golly, the biggest jump is from Year One to Two."

Caldwell seconds that emotion. "That's where they make the biggest jump," he says.

Buffalo Bills fans are hoping for that. E.J. Manuel is embarking on his second season and the Bills moved up in the draft to get wide receiver Sammy Watkins to provide their young QB with a weapon.

McCown thinks the hardest part about learning the most challenging position in the game is that "there are so many moving parts. You have to have your finger on the pulse of how guys are doing, there's a leadership aspect to the position and also an Xs and Os aspect. It's just being able to study and balance those and not get too caught up in doing one over the other.

"All of that said, it's also about dealing with adversity. â?¦ Sometimes you get caught up so much in what's going on on the field, maybe your technique slips. It's just knowing that playing this position, there's so much you have to know. It takes a long time."

And when there's an onrushing lineman, or an onrushing three-year window, a long time is something many young quarterbacks simply do not have.